Bean leaf beetles like the one pictured here can devastate soybean fields.
Now that much of the 2015 crop is in the ground, it’s time to think about management. Two pests farmers should be thinking about are black cutworms and bean leaf beetles.
The bean leaf beetle is a triple threat to soybeans. Beetles that have overwintered feed on young soybean plants in May and June, the first new generation of beetles appears in July. Some farmers may try and avoid the early-season threat by planting soybeans later may be doing more harm than good. The second and more detrimental generation of beetles peak during the pod-fill stages of growth and cause extensive damage to the plants. In addition to the multi-generational threats to soybeans the bean leaf beetle also transmits the bean pod mottle virus (BPMV) while it feeds. Increases in incidents of BPMV have correlated to bean leaf beetle populations.
Bean leaf beetles are present in most of the U.S. soybean-growing states. In areas where bean leaf beetle winter mortality is low and there is a known history of the beetles seed applied insecticides would be a good control option, as seen in this recent article from Iowa State University (ISU). Beetle numbers going into 2014 winter were down because of the harsh 2013-14 winter. With less beetles overwintering there are less to cause problems the following spring.
To determine if in-season control is needed, scouting is critical. The beetles themselves or defoliation are the main indicators of an issue. If a problem is discovered spraying an insecticide will generally give adequate control.
“In early planted soybean the neonicotinoid seed-applied insecticides give good control of bean leaf beetle,” said Tristan Mueller, operations manager of agronomic research for the Iowa Soybean Association (ISA) On-Farm Network. “Scouting is important for managing them and other early-season pests.”
Black cutworm feeds on young corn plants. Damage usually begins as pinhole feeding on young corn leaves. As the cutworm grows, damage will evolve to full and partial plant cutting. Corn over V5 to V8 may still receive damage to the growing point. The threat to yield comes from the significant and often erratic reduction in stands.
Black Cutworms overwinter in the south as larvae and are blown into Iowa as moths during spring outbreaks of warm weather with strong southerly winds. ISU has been catching black cutworm moths in traps since early April, see their results here. The traps use a pheromone lure to attract the adult moths to the sticky board within. Just because moths are being caught doesn’t necessarily mean there will be an infestation that has an effect on yields. Other states experiencing black cutworm moths include Minnesota, Illinois, Indiana, Missouri and Kentucky.
Scouting is important to controlling the damage done by black cutworm. Being aware of moth flight patterns will allow farmers to possibly predict when their eggs will hatch and potentially cause problems. Don’t assume that corn insect traits will make your stands exempt from damage. Black cutworm management is most often conducted in-season with an insecticide applied to infested areas.
“Cutworm infestations don’t often cover whole fields, but in the isolated patches where damage occurs the stand reduction is often visible,” said Rich Stessman, ISA On-Farm Network field research specialist for NW Iowa. “The best defense is to scout early and take action before cutting occurs, if the level of infestation justifies it.”
The crop for 2015 has just gotten started. With proper management of early-pests the risk of them impacting yield is reduced. For continued updates throughout the growing season, look for future Advance articles.